The present invention relates to oxygen-alkylated and/or oxygen-acylated coal and coal bottoms.
Coal, once the leading source of energy in the United States, is beginning to play a more important role in the nation's energy future. The primary reason for the growing importance of coal is the rapid depletion of known petroleum and natural gas reserves. These known reserves are being depleted at a rate considerably faster than the rate of discovering new reserves. As the era of petroleum growth draws to a close, the world's energy mix will have to change. Transition energy sources will be needed as a bridge between petroleum and the potentially unlimited energy sources of the furture; such sources being, for example, solar power and nuclear fusion. Owing to its great abundance, coal is perceived as one of the keystones of such a bridge. Consequently, much work is presently in progress to provide economical ways of converting coal to valuable liquids and gases as well as to ways of chemically modifying the structure of coal in order to produce a coal having greater utility than coal not so modified.
Processes for the liquefaction of coal and similar carbonaceous solids usually involve contacting the feed material with a hydrocarbon solvent and molecular hydrogen at elevated temperature and pressure. This results in partial breakdown of the complex high molecular weight starting material into lower molecular weight hydrocarbon liquids and gases. These are recovered from the liquefaction effluent, leaving a heavy liquefaction bottoms product which normally boils in excess of about 550.degree. C. and generally contains suspended solid residues. The liquefaction bottoms may constitute 50% or more by weight of the total liquefaction products.
A variety of processes for upgrading liquefaction bottoms have been proposed in the past. Exemplary of these include pyrolysis of the bottoms that produce gases, additional hydrocarbon liquids and coke, followed by steam gasification of the coke to form hydrogen and carbon monoxide for use as a fuel; see e.g., U.S. Pat. No. 4,060,478. Another process for upgrading liquefaction bottoms is disclosed in U.S. Pat. No. 4,089,772 which discloses an acid-catalyzed C-alkylation of C-acylation of liquefaction product bottom prior to recycling the bottoms fraction to the liquefaction reaction zone.
These various processes result in more efficacious use of liquefaction bottoms. However, during subsequent coal liquefaction process, phenols present in the coal are cleaved to produce water. In liquefaction processes employing hydrogen, an excessive use of hydrogen thus occurs.
Solvent extraction of coal also leaves behind a high molecular weight, insoluble fraction of coal called coal solubilization bottoms. Like liquefaction bottoms, this heavy fraction is also the object of various upgrading processes in order to obtain increased liquid yields.